A 23-year-old woman convicted of adultery will be stoned to death unless granted a last minute appeal by authorities in Sudan.

Laila Ibrahim Issa Jamool is being kept shackled to her six-month-old baby after being convicted by a court in the capital Khartoum on July 10, activists say.

President Omar Hassan al-Bashir said last month Sudan would adopt a "100%" Islamic constitution after the breakaway of non-Muslim South Sudan a year ago.

Jamool's husband accused her of 'Zina' (adultery), illegal under the Sudan Penal Code 1991. Her death sentence is the second to be passed in Sudan for the offence in the last few months.

Her case is being followed closely by the Strategic Initiative for Women in the Horn of Africa (SIHA), a women's rights group. They have assigned lawyers who have appealed against the conviction and sentence.

"The appeal is understood to take not less than one-and-a-half months before a response can be got from the court of appeal," SIHA said in a statement.

"During all this time, Mrs Jamool will still be shackled in Omdurman women's prison together with her six-month-old child."

Amnesty International said the conviction did not meet international legal standards and also violated Sudanese criminal law.

"The stoning sentence was imposed after an unfair trial in which she was convicted solely on the basis of her confession and did not have access to a lawyer," Amnesty said in a statement.

Floggings are a common punishment in Sudan for crimes such as drinking alcohol and adultery. But sentences of stoning are rare. Officials in Sudan's justice and information ministries were not available for comment.